The interface between water and Langmuir films of long chain aliphatic molecules is investigated using accurate intermolecular potentials. The stabilities of various ice structures which could form at the interface are examined. Antiferroelectric ice is found to be the most stable, but this stability depends crucially on the first layer of water. Ferroelectric structures are found to collapse upon relaxation. Our model was not able to differentiate between the different nucleation properties of C31H63OH and C30H61OH. A better description of the alcohol-water interaction is probably required to account for this difference. (C) 2003 American Institute of Physics.